Wyatt grew up in Ithaca, NY where he attended Ithaca High School, graduating in 1986. He had been playing role-playing games since the late 1970s, beginning with the first Basic D&D set: "I remember pretending to be a wizard in my backyard before I picked up the basic set... I used the monster statistics in the D&D books to give us wizards something to fight in our primitive backyard live-action roleplaying game." After high-school he attended Oberlin in Ohio as a religion major and graduated in 1990. He went on to receive a Master of Divinity from Union Theological Seminary in New York City, in 1993. He married his wife, Amy, soon after. In 1994 Wyatt began his working career as the minister of two small United Methodist churches in southeastern Ohio.
While working as a minister Wyatt began writing in his spare time for Dragon magazine, starting with material for TSR's Masque of the Red Death setting. By 1996, Wyatt decided to change his career path: "While I was in the ministry, I started submitting adventures to Dungeon magazine... I found that my D&D work was a source of freedom and energy when ministry was more life-draining for me. When I started getting adventures and articles accepted, it was so exciting that it became clear that D&D would never again be just a hobby for me." The same year he moved to Wisconsin in hopes of getting a full-time job at TSR, which did not immediately work out, but he kept writing material as a freelance author. Wyatt produced work for roleplaying games such as West End's Hercules and Xena, although he felt that "D&D has always been my one true love in the gaming world... despite junior high flings with other game systems." He continued to have material published in Dragon and Dungeon.
In 1998 he moved to Berkeley, California, and in 2000 to the Seattle/Tacoma area of Washington state. Wizards of the Coast ultimately hired him in January 2000 to work on the D&D game full-time; his first assignment was Monstrous Compendium: Monsters of Faerûn, of which he wrote two-thirds. His other early works for Wizards of the Coast included The Speaker in Dreams (a core adventure on the original Adventure Path, following The Sunless Citadel and The Forge of Fury), Defenders of the Faith, the monsters chapter in the Forgotten Realms Campaign Setting, and numerous articles in Dragon and Dungeon. Wyatt wrote Oriental Adventures (2001), a setting book that Wizards had in process for over a year, and which offered new rules for Oriental realms, some of them specific to the world of Rokugan. He wrote City of the Spider Queen and co-authored numerous roleplaying game products, including Magic of Incarnum, Sharn: City of Towers, Draconomicon, The Book of Dragons, and Book of Exalted Deeds. Eberron was introduced with the Eberron Campaign Setting (2004), produced by Keith Baker alongside Wyatt and Bill Slavicsek. Early in 2005, Slavicsek organized a team to work on some early designs for a fourth edition of D&D, which was headed up by Rob Heinsoo and also contained Collins and Wyatt; Heinsoo, Collins, and Wyatt formed the core fourth-edition team. Wyatt was on the SCRAMJET team, led by Richard Baker, and including Matt Sernett, Ed Stark, Michele Carter, Stacy Longstreet, and Chris Perkins; this team updated the setting and cosmology of D&D as the fourth edition was being developed.
He wrote the D&D novels In the Claws of the Tiger (2006), Storm Dragon (2007), Dragon Forge (2008), Dragon War (2009), and Oath of Vigilance (2011).
As of April 2016, he has left Dungeons & Dragons and now works on the writing and creative aspects of Magic: The Gathering.
Wyatt received Origins Awards in 2003 for City of the Spider Queen and in 2005 for the Eberron Campaign Setting, which he co-authored with Bill Slavicsek and Keith Baker. His other notable works include Oriental Adventures (for which he won an ENnie Award in 2002), Draconomicon, the Draconic Prophecies series, and Magic of Incarnum.